KR20000052848A - Quadaxial gradient index lens - Google Patents

Abstract

PURPOSE: A lens is provided which has the ability to gather and focus light to a spot with a minimum of spherical aberration and with a substantially uniform distribution of light intensity from center to periphery of the spot, in particular, a square spot size. CONSTITUTION: An axially-based lens is provided, comprising two biaxial elements(66,68), each having entrance and exit surfaces(18,20). The exit surface(20) of one(66) of the elements is joined to the entrance surface of the other element(68), with one of the elements rotated at an angle with respect to the other. In a preferred embodiment, the angle of rotation is 90°. The axially-based lens thus comprises four axial sub-elements, and is called a "quadaxial" lens herein. The axially-based lens element has the ability to gather and focus light to a spot with a minimum of spherical aberration and with a substantially uniform distribution of light intensity from center to periphery of the spot. In a preferred embodiment, the lens element focuses light to a square spot size.

Description

4-axis gradient refractive index lens {QUADAXIAL GRADIENT INDEX LENS}

A coupler is an optical element for connecting a light source such as a laser diode, a light emitting diode, an optical fiber or another light source to a light receiver such as a photo detector, an optical fiber, an optoelectronic chip, an optical fiber, or the like.

Prior art couplers include (1) homogeneous glass lenses, (2) radially distributed refractive index glass cylinders or rods. Homogenous glass lenses require an air layer and have low numerical apertures or light receiving values, so that less light is transmitted to the receiver than light incident on the coupling lens. In addition, homogeneous glass or plastic lenses cannot correct aberrations, resulting in inefficient coupling unless a spherical surface is formed on the lens. Finally, multiple devices are needed to fully connect the light.

The radially distributed refractive index glass cylinder lens functions as a flat surface and focuses light at the lens exit surface, thereby overcoming one of the problems of homogeneous glass lenses. Furthermore, the radially distributed refractive index glass cylinder lens comprises a single light component, thereby overcoming other problems of homogeneous glass lenses. However, these radially distributed refractive index glass cylinder lenses cannot form small focal points, resulting in inefficient coupling performance. Coupling performance can be improved by forming a curved surface on the exit surface of the lens, while the advantages of the flat surface are lost and an air layer is introduced into the coupling mechanism.

In operation, the radial rod lens starts incident light into focus, and then the image is dispersed, refocused, or the like until it is present in the rod. The problem when light is incident across the diameter of the rod is to determine what is the distance to the focal point. In other words, the intermediate rays travel longer through the material and feel the same power effect than the outer or edge rays, so that these rays are focused at different locations than the edge (extreme) rays. In the area of the first focal point, the beam dispersion is not as bad as the other lengths but the spot size becomes much larger. The large spot size is due to aberrations, which necessitates correcting the curved exit surface or at least one additional lens element.

Gradient optical elements known as biaxial lenses are disclosed in US patent application Ser. No. 08 / 400,804, filed March 8, 1995. This biaxial lens is formed of an optical material and has a plane-plane incidence and exit surface and an optical axis therebetween. The optical material has a refractive index that varies symmetrically about a central plane including the optical axis, the refractive index being substantially constant in a direction parallel to the central plane.

Biaxial lenses are manufactured by first forming a subelement having a gradient of refractive index from the first surface to the second surface, both surfaces being perpendicular to the incident and exit surfaces. All surfaces of the subelements are flat. Thus, the subelement has a gradient of refractive indices that starts at a lower value L and ends at a higher value H. These two sub-elements are joined together along a low or high refractive index surface to form a high-low-high (H-L-H) form or a low-high-low (L-H-L) form, respectively. Such biaxial lenses are used instead of cylindrical lenses to form a linear focus.

Therefore, there is a need for a lens that can collect light and focus light into a spot having minimal aberration and a substantially constant light distribution from the center to the periphery of the spot. In particular, a square spot size is needed.

Summary of the Invention

According to the present invention there is provided an axially based lens comprising two biaxial elements, each element having an entrance and exit surface perpendicular to the refractive index gradient. The exit surface of one of the devices is coupled to the entrance surface of the other device, and one of the devices is rotated at an angle with respect to the other device. In a preferred embodiment, the rotation angle is 90 degrees. Thus, an axially based lens comprises four axial sub-elements, referred to herein as a "quadaxal" lens.

The lens element based on the axial direction of the present invention can collect light and focus light into a spot having a minimum aberration and a substantially constant light distribution from the center to the periphery of the spot. In a preferred embodiment, the lens elements form a square spot size.

Other objects, features and advantages of the present invention will become apparent upon reference to the following detailed description and accompanying drawings, wherein like reference numerals refer to similar features throughout the figures.

The present invention relates to an optical element, and more particularly to a lens comprising a sub element having a gradient of refractive index along the axial direction.

It is to be understood that the drawings referenced in this description are not to scale unless specifically indicated.

1A shows a prior art axial gradient lens having the above-described refractive index change,

FIG. 1B graphically illustrates an exemplary refractive index profile for the axial gradient lens shown in FIG. 1A, with coordinates in the refractive index and thickness;

FIG. 2A illustrates a prior art biaxial gradient lens comprising two axial lens elements coupled along each high refractive index surface; FIG.

FIG. 2B graphically illustrates an exemplary refractive index profile for the biaxial gradient lens shown in FIG. 2A, the coordinates being indices of refractive index and thickness, FIG.

FIG. 2C shows a prior art biaxial gradient lens comprising two axial lens elements coupled along each low refractive index surface; FIG.

3A is a side view of a four axial dispensing coupler component of the present invention comprising two biaxial dispensing components rotated 90 ° with respect to one another and joined end to end;

FIG. 3B is a top view of the four axial distribution coupler component shown in FIG. 3A;

3c shows the resulting line focal point, a cross sectional view of the dispensing component on the first two axes,

FIG. 3A illustrates the resulting rectangular focal spot resulting from the use of a flat or planar surface, a cross-sectional view of the four axial distribution coupler component shown in FIGS. 3A and 3B;

4A is a perspective view showing the orientation of two biaxial distributing coupler components before being joined to form a four axial distributing optical element of the present invention;

FIG. 4B is a perspective view of a four axial distributing optical element after joining together the two biaxial distributing coupler components shown in FIG. 4A;

5A shows a four-axis lens of the present invention with an injection surface bent to form a parabolic, more precisely circular spot shape, FIG.

FIG. 5B is a cross-sectional view of the four axial distribution coupler component shown in FIG. 5A showing the resulting circular spot made by using a curved injection surface. FIG.

Reference will now be made in detail to certain embodiments of the present invention in order to illustrate the best mode presently anticipated by the present invention for practicing the present invention. In addition, it is described simply that the modified embodiment can be applied.

The axial distribution refractive index of the refractive index lens, sometimes referred to in the prior art as a distributed refractive index lens (GRIN lens), is a flat glass slab, with predesigned refractive index fluctuations within the flat glass slab that provide the function of an analog lens array; Such examples are disclosed on pages 44-47 of P.K.Manhart's "Optics and Photonics News (March 1995)." The single-axis refractive index lens manufacturing technology available from LightPath Technologies, Inc. of Albuquerque, New Mexico, USA, has revolutionized the imaging industry. The lens is available under GRADIUM®.

Producing an axial GRIN lens blank is disclosed elsewhere. See, for example, U.S. Patent No. 4,929,065 and Siaji J. of July, August, 1994. Xiaojie J. Xu et al., Entitled "Preparation of Macro Axial Gradient Refraction Glasses" by the Gradient Index Optical Systems-Topical Meeting in Rochester, NY, USA The document discloses stacking a plurality of glass plates, each glass plate being of a different composite to form a stack in which the focus is formed so as to cause mutual blur of the elements of the composite at a sufficiently high temperature. Form a glass body. Specific profiles of the refractive index, such as linear, parabolic, square, cube, etc., can be achieved by controlling the thickness and the refractive index (composition) of the individual glass plates. Thus, the desired profile can be formed by calculating the plate thickness and refractive index as disclosed in US Pat. No. 4,929,065.

Alternatively, the glass mixture may be used to form the lens blank. In this case, the desired profile can be produced based on the weight of the mixture with a certain refractive index (composition). Knowing the density of a particular glass composition allows the thickness of the plate to be converted to weight. This method is the subject of US patent application Ser. No. 08 / 441,275, filed May 15, 1995, which was assigned to the applicant.

The monolithic glass body or boule formed by heating the glass plate or glass mixture to a sufficiently high temperature for a period of time is core-drilled to provide multiple glass blanks and then ground and polished to provide a lens. It can be formed from a variety of lens surfaces, including planar, concave and convex surfaces and combinations thereof.

1A and 1B are schematic diagrams of changes in refractive index along the axis 116 (along the cross-section). As shown in FIG. 1A, the glass blank 110 has a low refractive index face 112 and a high refractive index face 114. The face 112 of the blank 110 is formed of a material having the lowest refractive index in the stack, and the opposing face 114 is formed of a material having the highest refractive index. The refractive index varies between the two faces 112 and 114 in some of the forms described above. Preferably, the profile is parabolic. An example of a profile is shown in FIG. 1B as being a half parabolic curve 118.

The next step is to carefully orient, grind, and polish the low and high refractive index faces 112, 114 of the glass blank 110, respectively. In addition, optical properties such as gradient refractive index profiles are typically measured during this step.

Thereafter, the blank 110 is cut into two portions perpendicular to the isoindex plane. To produce a biaxial element, the two parts are joined together and their high index face 114 or low index face 112 are joined. However, it is desirable that these surfaces be polished and slightly concave before the surfaces are joined. For a surface of about 4 cm 2, the curvature shown by ten rings on the optical plane with green light is acceptable for this purpose. After the surfaces have been polished, the surfaces can be cleaned in an ultrasonic methanol bath for 10 minutes, cleaned with distilled water to remove mineral deposits, and then heated and maintained to fuse them together. Optionally, the two surfaces can be joined together using an optical binder with a suitably matched refractive index.

The cylindrical gradient lens 140 has a gradient refractive index only along one axis 150 orthogonal to the optical axis 152 of the lens. Lens 120 has flat front and back surfaces 142, 144 and can act as a cylindrical lens that focuses light with straight line 148 in two-dimensional image 146.

If the high refractive index face 114 is combined, the resulting block 120 has a central region 122 of material with high refractive index. From this central region 122, the refractive index is reduced towards the end 124 of the block 120. The resulting refractive index profile across the width of block 120 is shown by curve 126 in FIG. 2B. This curve 126 can be expected is a combination of the two curves 118 shown in FIG. 1B. In order for the block 120 to act as a cylindrical axial distribution lens focusing light in a line such as line 148 in FIG. 2A, the curve 126 of the refractive index profile is substantially quadratic or parabolic. Should be However, other profile shapes may also be used in other applications.

If the low index face 112 is combined, the resulting blank or lens blank 130 of optical material becomes as schematically shown in FIG. 2C. In this lens blank 130, the central region 132 has the lowest refractive index, while the outer edge 134 has the highest refractive index as opposed to the situation just described. The resulting profile of the refractive index is a combination of the two curves 118 shown in FIG. 1B, but is the opposite of the case where the high refractive index face 114 is combined. Depending on the intended field, the profile may be quadratic or parabolic.

Referring now to FIGS. 3A-3D, 4A, and 4B, the four-axis distribution optical coupler 10 includes a planar incident surface 18 and a planar exit surface 20, with an optical axis 22 therebetween. It is a single component 24 comprising a four-axis distributed refractive index element with. The four-axis distributed refractive index element includes two biaxial distributed refractive index sub-elements 66 and 68. Each subelement 66, 68 has two axially distributed refractive index sub-subelements each having a gradient refractive index starting at a lower value L on one surface and ending at a higher value H on the opposite surface. 56, 58, 156, 158). The two sub-subelements 56, 58, 156, 158 are joined together at a surface having a higher refractive index value, the combined surfaces being perpendicular to the incident and exit surfaces 18, 20. Two biaxially distributed refractive index sub-elements 66, 68 are joined together along the exit surface 20 'of one sub-element 66 to the incident surface 18' of the other sub-element 68, one The subelement of is rotated 90 ° about the optical axis with respect to the subelement. A detailed description of combining two subelements is shown in FIGS. 4A (before combining) and 4B (after combining).

Light passing through the first sub-element 66 is focused on a line 70 having a finite width as shown in FIG. 3C. After passing through the second sub-element 68, the light is focused on a rectangle 72 having a side length equal to the width of the line 70 as shown in FIG. 3D. As a result, the output from the light source 12 is approximately symmetric about the x and y axes.

5A shows a four-axis lens with a convex spherical ejection surface 20 ". This surface surrounds the focal spot 72 as shown in FIG. 5B.

For all the lenses described above of the invention, the preferred profile is a parabolic profile. The Δn used may be any suitable value except that smaller Δn requires a larger overall lens size.

A very important additional feature is to position the diffracted light surface on the surface of the axially distributed refractive index element or between the elements to provide an additional degree of freedom to correct the aberration along the optical axis of the lens shape described above and / or To allow focusing and / or collimation of light through the lens described above in additional dimensions. This lens places the diffraction element on a predetermined surface in the material of the epoxy material, and then another axially distributed refractive index element of the biaxially distributed refractive index element with an optical element having a refractive index significantly different from that of the epoxy material. It is formed by adhering to.

This allows for the combination of switchable lasers without altering the optical path difference (OPD), and in two or more directions: ① through the optical axis, ② at an angle of 90 ° from the optical axis, and ③ above described diffraction and / or holographic light The use of the device makes it possible to focus light simultaneously from two light sources at an angle of 45 ° to the optical axis which can be achieved.

In addition, an active material can be added to the lens described above, in which the diffraction rate can be adjusted to provide an optically transparent signal or focus shift function.

The four-axis distribution optical element can be used in various fields for collecting, focusing, collimating and connecting light with or without air layers with high numerical apertures and near constant distribution of light intensity, and where the curved surface is undesirable. It is expected to be possible.

Thus, a four-axis lens has been disclosed. Those skilled in the art can readily appreciate that various modifications and alterations of obvious nature and all such modifications and variations are within the scope of the invention as defined in the appended claims.

Claims (9)

A four-axis lens comprising a first biaxial element and a second biaxial element connected together, each biaxial element having an incidence and exit surface perpendicular to the optical axis, the first two The ejection surface of the axial element is coupled to the incident surface of the second biaxial element, one of the biaxial elements being rotated relative to the other biaxial element and the first biaxial direction The element is configured to form a line focus at its exit surface and the second biaxial element is configured to form a spot focus at its exit surface such that the 4-axis lens has a minimum aberration and from the center of the spot. To collect and focus light in a spot with a light intensity that is substantially uniformly distributed to the periphery 4-axis lens. The method of claim 1, The optical axis is perpendicular to the refractive index gradient 4-axis lens. The method of claim 1, The first biaxial element is rotated 90 ° with respect to the second biaxial element. 4-axis lens. The method of claim 1, The injection surface is planar 4-axis lens. The method of claim 4, wherein The first biaxial element has a first Δn, and the second biaxial element has a second and different Δn, whereby the spot is rectangular 4-axis lens. The method of claim 5, The first and second Δn are the same, whereby the spot is rectangular 4-axis lens. The method of claim 1, The injection surface is curved 4-axis lens. The method of claim 7, wherein The first biaxial element has a first Δn, and the second biaxial element has a second and different Δn, whereby the spot is elliptical. 4-axis lens. The method of claim 8, The first and second Δn are the same, whereby the spot is circular 4-axis lens.